Silicon is the main semiconductor material used to fabricate today's commercial solar cells. The majority of commercial solar cells are fabricated from a monocrystalline or multi-crystalline silicon wafer. A p-n junction is formed in the silicon wafer by, for example, diffusing n-type atoms into a p-type silicon wafer.
A large proportion of solar cells are fabricated using a boron-doped wafer (p-type). Generally, the performance of a solar cell degrades when it is exposed to radiation or more broadly, subject to carrier injection. These phenomena are known in the art as Light Induced Degradation (LID) and Carrier Induced Degradation (CID).
In the photovoltaic industry, Passivated Emitter Rear Contact (PERC) solar cells are becoming increasingly popular because they deliver good potential for high-volume manufacturing at low cost and increased efficiency compared to conventional technologies. PERC solar cells are largely fabricated using multi-crystalline silicon (mc-Si) wafers. In the case of mc-Si wafers, the lifetime of charge carriers degrades significantly over long time scales due to CID. CID reduces the efficiency of PERC solar cells and it is known to occur much faster with increasing illumination intensities or at elevated temperatures.
Methods have been proposed to mitigate the detrimental effects of CID on solar cells. For example, it has been reported that eliminating the contact firing step during manufacturing largely reduces the effects of CID on cell performance. However, the solutions proposed are either not compatible with cell manufacturing processes, or provide limited improvement. For example, during the fabrication of screen printed mc-Si PERC solar cells, a firing temperature of 800° C. is commonly used in the art to form the silver-screen printed contacts.
There is a need in the art for a manufacturing process which is capable of stabilising the solar cells by substantially reducing the effect of CID on cell performance.